In the past, most commercially available cars have been powered by a combustion engine. One step to optimize fuel efficiency is to install a mild parallel hybrid drive. Such parallel hybrid drives comprise a combustion engine being coupled mechanically with the wheels of at least one of the front and rear axles. The mechanical coupling usually comprises at least one clutch coupling the output shaft of the combustion engine and to the input shaft of a transmission gear, (briefly gear). The output shaft of the gear is coupled via a differential gear (briefly differential) and drive shafts with the wheels. In addition an electrical machine is coupled to the wheels. Accordingly, drive power can be provided to the wheels by the electrical machine and as well by the combustion engine, i.e. ‘in parallel’. The electric energy for powering the electrical machine is provided by a battery.
In mild parallel hybrid cars, the battery (as synonym for at least one battery or the battery system) and the in most cases as well the electrical machine are dimensioned to only support the combustion engine, to thereby enable operating the combustion engine to an enhanced extent in its most efficient power regime. Additionally the electrical machine is used as booster for short time high power demands. The additional electrical machine thus enables installation of a smaller combustion engine without the electrical machine.
In the P0-configuration the electrical machine is coupled to the output shaft e.g. the crankshaft at the combustion engine's front, i.e. at the side of the combustion engine that is facing away from the clutch. In the P1-configuration the electrical machine is coupled to the same output shaft, but at the combustion engine's rear, i.e. at the side of the combustion engine that is facing towards the clutch. In the P1-configuration the electrical machine is between the clutch and the crankshaft. So to speak one may say that in both the P0- and in the P1-configuration the electrical machine is coupled to the output shaft of the combustion engine.
In the P0- and P1-configurations the electrical machine can start the combustion engine, thus an additional starter can be omitted. The electrical machine can as well be used as a generator for loading the batteries, if the combustion engine drives the electrical machine. The electrical machine may as well be used as a brake system to convert kinetic energy into electric energy, usually referred to as recuperation. For recuperation, the clutch between the wheels and the output shaft of the combustion engine must be closed.
To save fuel, cars with a P0- or P1-configuration are often configured for ‘coasting’. ‘Coasting’ means to decouple the combustion engine from the wheels, e.g. by opening a clutch when the mechanical power demand is low, e.g. downhill or when approaching a traffic light or a stop sign. During coasting the combustion engine may be temporarily shut-off, e.g. by cutting off fuel supply by keeping fuel injection nozzles, commonly referred to as ‘injectors’ closed. However, in this case the power for auxiliary systems like for servo steering, brake servo, air conditioning, lights etc. must be provided by the car's battery. If the state of charge (SOC) of the battery is low, the combustion engine can idle or spin slightly faster, only to drive the electrical machine, which in turn provides electrical power for supplying the auxiliary systems and/or for charging the battery.
Only to avoid ambiguities, an electrical machine at least enables to convert electric energy into mechanical energy, it may thus be used as electric motor. The electrical machine may as well be configured to convert mechanical energy into electrical energy. It may thus as well be used as generator. In some textbooks an electrical machine may as well be a transformer for converting a voltage of an AC-power source into another voltage, but this is not intended here. In this patent an electrical machine is an electric motor that optionally may be used as generator.